1. Technical Field
The present invention relates to a printer, such as a facsimile machine, a copier or other OA equipments, a printer control program and a printer control method, and more particularly, to a printer, a printer control program, a printer control method, a print data generating device, a print data generating program, and a print data generating method, which are adaptable for a so-called inkjet-typed printing process in which characters and/or images are printed on a print paper (recording material) by discharging particles of liquid ink having several colors on the print paper.
2. Related Art
Hereinafter, a printer, particularly a printer employing an inkjet method (hereinafter referred to as an inkjet printer) will be described.
In general, since inkjet printers are inexpensive and can easily produce color prints of high quality, the inkjet printers have widely spread to ordinary users as well as offices with increasing spread of personal computer, digital cameras and so on.
In such inkjet printers, in general, while a moving body, which is called a carriage or the like which includes an ink cartridge and a print head which are integrally formed, reciprocates on a print medium (paper) in a direction perpendicular to a paper feed direction, desired prints are produced by discharging (jetting) particles of liquid ink in a dotted shape from nozzles of the print head. The carriage may have four ink cartridges having four different colors (black, yellow, magenta and cyan) and respective print heads to allow full color print as well as monochrome print (in addition to this four-color print, six-color, seven-color print or eight-color print, including light cyan, light magenta and the like, is also putting to practical use).
However, in such inkjet printers in which the printing operation is performed while reciprocating the print head of the carriage in the direction perpendicular to the paper feed direction, the print head has to be reciprocated several tens times or more than 100 times in order to clearly print one page throughout. In other words, these inkjet printers have a drawback in that it takes even longer time to complete the printing operation than printers of different types, for example, laser printers or copiers employing an electrophotography.
On the other hand, in inkjet printers in which a long print head having the same width as a print paper is disposed without using a carriage, a so-called one scan (one pass) printing operation is possible without need to move the print head in a width direction, thereby allowing high speed print like the laser printers. In addition, since these inkjet printers require no carriage and no driving system for driving the carriage, they have an advantage of small-size, light weight, high silence. An inkjet printer of the former type (i.e., with carriage) is commonly called a “multi-pass type printer or “serial printer”, while an inkjet printer of the latter type (i.e. without carriage) is commonly called a “line head type printer.”
A print head essential to the inkjet printer is arranged in one or more rows in a printing direction with fine nozzles having a diameter of 10 to 70 μm or so disposed at specified intervals. Therefore, an ink discharge direction of some nozzles may be inclined or positions of nozzles may be deflected from their ideal positions due to their manufacturing errors. This may result in a so-called “flying deflection” effect that impact positions of dots formed by the nozzles are deflected from their ideal positions. In addition, if the nozzles are disposed very irregularly, the amount of discharged ink may be very larger or very smaller than the ideal amount.
As a result, there may occur a print defect, which is called a “banding (stripe) effect,” in a portion printed by the defective nozzles, which results in noticeable deterioration of print quality. That is, if the “flying deflection” effect occurs, as a distance between dots discharged by adjacent nozzles becomes irregular, a “white stripe” (in case of white print paper) occurs in a portion where a distance between adjacent dots becomes abnormally long, while a “thick stripe” occurs in a portion where the distance between adjacent dots becomes abnormally short. In addition, when the amount of discharged ink is different from the ideal amount, the thick stripe occurs in a portion of print paper corresponding to a nozzle discharging a high amount of ink while the white stripe occurs in a portion of print paper corresponding to a nozzle discharging a low amount of ink.
Particularly, such a banding effect is apt to occur in the line head type printer in which the print head or the print medium is fixed (one pass print), rather than the multi-pass type printer (or the serial printer) (the multi-pass type printer may remove the banding effect by reciprocating the print head many times).
In order to prevent a kind of print defect by such a banding effect, although research and development have actively made to improve a hardware part, for example, a print head, it is difficult to provide a print head with no banding effect in the respect of manufacture costs and technique.
At present, accompanied with the improvement of the hardware part, a software method has been used to reduce the banding effect. Several examples of the software method are as follows.
For example, JP-A-2002-19101 and JP-A-2003-136702 disclose a technique in which a shading correction method is used in a portion of print paper having low print density to cope with irregularity of a print head while a color is substituted with a different color (for example, a black color is substituted with a cyan or magenta color) in a portion of print paper having high print density to remove the banding effect or print irregularity.
As another example, JP-A-2003-63043 discloses a technique in which a beta image (an image so painted throughout as not to view a base) is generated over all nozzles by increasing the discharge amount of ink of adjacent nozzles of neighboring pixels of nozzles that can not discharge ink.
As still another example, JP-A-5-30361 discloses a technique in which a degree of irregularity of nozzles is fed back to error diffusion and a banding effect is avoided by absorbing the irregularity of the discharge amount of ink of the nozzles.
However, in the related techniques disclosed in the above Patent Documents 1 to 4, since a banding prevention process to reduce deterioration of image quality by the banding effect is performed for only a portion to be corrected (a portion where a banding effect occurs), there may occur a visual difference between an image of a corrected portion and its adjacent images. In other words, the deterioration of the image quality may be more remarkable in the portions having such a difference than that before the banding prevention process.